The present invention relates to a method and apparatus for coding a moving image signal by using a band compression technique.
As a conventional scheme for coding a moving image signal by using a band compression technique, for example, a scheme described in "Color Moving Image Videophone Compatible with ISDN", Spring National Convention of the Institute of Electronics and Communication Engineers of Japan, Reference No. D-233, 1989 is known. In this scheme for coding a moving image signal, a face region is extracted from a frame to form a map. In an image coding section, inter-frame and intra-frame adaptive prediction operations are performed. In this case, if a face region is determined, coding is performed to the last step. Otherwise, coding is stopped in a step immediately preceding the last step to reduce the coding amount.
In the above-described conventional scheme for coding a moving image signal, however, since a background portion other than a face portion is coarsely coded, unnecessary information is generated because of noise in the background portion. In addition, if a background portion is changed to a face portion between continuous frames, since a coarsely coded portion is changed to a finely coded portion, a large number of predictive error signals are inevitably generated. That is, unnecessary information is coded. As a result, the coding efficiency is decreased.